This invention relates to a fluid drive system for a vehicle, and in particular to a fluid drive system having energy regeneration and storage capabilities. This system employs existing technology and a novel arrangement that in one embodiment provides both hydraulic and pneumatic systems, which extract kinetic energy from the vehicle as it is decelerating or braking. The system converts the kinetic energy to both stored pressurized hydraulic fluid and to stored electrical energy, which both can be used to power the fluid drive system.
In an effort to conserve resources and reduce environmental impact, numerous vehicles and drive systems have been developed including electrical vehicles, hydraulic vehicles, and hybrid vehicles which use a combination of power sources, such as electrical power and an internal combustion engine. The challenge continues to be how to provide increased range and power for the vehicles and to increase the efficiency of energy regeneration systems and minimize power loss.
It is well known to provide both AC and DC drive motors on an electrical vehicle. Furthermore, one method that is well known for trying to increase the range of an electrical vehicle is to provide a regenerative braking system. A regenerative braking system captures a portion of the kinetic energy in a moving vehicle during deceleration. As the vehicle is decelerating, the electric motor of the vehicle is used to provide a kinetic braking force and is operated as a generator used to generate electrical energy to recharge the energy storage system. Of course, a separate generator may also be used to provide the braking force as opposed to the electric drive motor of the vehicle. The electrical energy produced by the regenerative system is stored in the vehicle energy storage system and is used to power the vehicle's electric motor to increase the range. One limitation of typical regenerative braking systems are that they can only generate electricity while the vehicle is still moving, and are not designed to generate any electricity once the vehicle has come to a stop or when the vehicle is accelerating. Also, it is believed that typical regenerative braking systems are only about 5–10% efficient in returning energy back to the batteries. Furthermore, the rate of charge to the batteries may spike immediately during regenerative braking and then decline rapidly. This may be detrimental to the life span of the batteries and associated electronics. Examples of regenerative braking systems are found in U.S. Pat. No. 6,033,041 to Koga, et al.; U.S. Pat. No. 6,222,334 to Tamagawa, et al.; U.S. Pat. No. 6,490,511 to Raftari, et al.; U.S. Pat. No. 6,497,635 to Suzuki; and U.S. Pat. No. 6,518,732 to Palanisami which are fully incorporated herein by reference.
It has also been disclosed to provide a charging system for an electrical storage system or batteries for a system, using a compressed fluid, a turbine operated by the compressed fluid, and a generator driven by the turbine, as is shown in U.S. Pat. No. 6,054,838 to Tsatsis, incorporated fully herein by reference. The compressed fluid, such as air, is stored in a pressure storage tank and is released through a venturi to raise the pressure of the fluid entering the turbine. Tsatsis also discusses providing a compressor system to provide compressed air. A motor is used to drive the compressor system. Tsatsis does not show or disclose any means, however, for generating the pressure to drive the turbine by using recycled kinetic energy from the motion of the vehicle.
Another system is disclosed in pending U.S. patent application Ser. No. 10/629,395 to Applicant filed on Jul. 29, 2003, the complete disclosure of which is hereby expressly incorporated by reference. This system discloses an electrical vehicle having a pneumatic regenerative system. The system includes an air compressor, a compressed air storage tank, a pneumatic motor, and a generator. The compressor is positively connected to a rotating assembly during the deceleration state of the vehicle to drive the compressor to fill the compressed air storage tank with compressed air. The compressed air is used to drive the pneumatic motor which in turn drives the generator for regenerating electrical batteries in the vehicle.
It is also known to use a hydraulic transmission system for powering a vehicle such as disclosed in U.S. Pat. No. 4,679,396 to Heggie, incorporated fully herein by reference. Heggie discloses a system with two variable displacement hydraulic pump units and a hydraulic unit coupled to the engine. It is also known to provide a pair of hydraulic tanks when using a hydraulic transmission system. One of the tanks is typically a low pressure or reservoir storage tank, and the other is a high pressure or accumulator tank. An accumulator is a tank that may be pressurized with nitrogen or other compressible gas and then filled with hydraulic fluid. As the fluid enters the accumulator and fills the tank, the gas is further compressed, which pressurizes the fluid. The pressurized fluid in the tank can then be used to operate a hydraulic motor. Examples of hydraulic systems employing both a reservoir tank and an accumulator tank are found in U.S. Pat. No. 4,760,697 to Heggie, et al., and U.S. Pat. No. 6,119,802 to Puett, Jr., which are fully incorporated herein by reference. Accumulator tanks in these systems are pressurized with the fluid pumped there during braking or deceleration of the vehicle to store a portion of the kinetic energy of the vehicle. The pressurized fluid is then available for assisting in powering the vehicle.
Stored kinetic energy, such as in an accumulator, may be used to provide the initial acceleration of a vehicle, which may greatly increase the range of the vehicle. In a vehicle using electrical energy, the electrical consumption is greatest in volume and rate during initial acceleration, causing most of the energy depletion and loss of range. Therefore, an accumulator assisted initial take-off system may prevent this condition by allowing for initial take-off without electrical loss or drain.
In addition, the number of batteries in an electrical vehicle must accommodate the electric demands of the vehicle, as dictated by the amount of energy required to propel the vehicle for the design range. With an accumulator system assisted take-off, as well as on board charging of electrical batteries, the number of batteries in an electrical vehicle may be minimized.
One prior art example of a fluid drive system that uses an accumulator tank to store kinetic energy as well as an on board electrical charging system is disclosed in U.S. Pat. No. 5,427,194 to Miller, which is incorporated herein by reference. The system in Miller only uses one hydraulic tank, which is a combined fluid reservoir and hydraulic accumulator. In addition, Miller discloses a fly wheel suspended by a magnetic force for driving a hydraulic motor/pump when the hydraulic accumulator source of reserve energy is exhausted. The fly wheel is driven by an electric motor receiving power from an array of electric batteries. When the vehicle stops, energy in the rotating fly wheel will continue to recharge the electrical battery through a generator attached to the shaft upon which the fly wheel rotates. Miller also discloses recharging the hydraulic accumulator using a hydraulic motor/pump when the vehicle is up to speed or coasting. Miller does not disclose being able to use the power from hydraulic motor/pump to generate electricity if the accumulator becomes fully pressurized. In addition, Miller does not disclose how to use a pneumatic system in combination with a hydraulic drive system to provide a dual energy storage system.